Project Summary - Project 2 Project 2 builds on our preliminary data and cumulative reports in the literature that have identified STAT3 as a target for therapy in HNSCC. Direct injection of a decoy oligonucleotide selectively targeting Signal Transducer and Activator of Transcription-3 (STAT3) into the HNSCC tumor in a phase 0 clinical trial completed during the current funding period demonstrated decreased expression of STAT3 target genes in the tumor. To overcome the requirement for repeated local injection, we chemically modified the STAT3 decoy to create a more stable, cyclic formulation that can be delivered intravenously with anti-tumor effects and no evidence of toxicity in mouse models. To maximize selective cyclic STAT3 decoy accumulation in the area with highest tumor burden, we are now investigating the potential of microbubble (MB) encapsulation of the cyclic STAT3 decoy, allowing systemic delivery coupled with tumor directed ultrasound to augment regional delivery of the cyclic STAT3 decoy. Site-directed ultrasound can be tuned to cause destruction of intravenously injected MBs resulting in release and delivery of the cyclic STAT3 decoy selectively into ultrasound-exposed tumor cells. To define predictive biomarkers for STAT3 targeted therapy, we will determine the contribution of loss of function genetic alterations of a key negative regulator of STAT3, protein tyrosine phosphatase receptor T (PTPRT), which we recently reported in HNSCC and other cancers. This project will have 3 aims to test the safety and feasibility of these approaches to STAT3 targeting: Aim 1: To conduct a phase I clinical trial of intravenous cyclic STAT3 decoy in patients with recurrent/metastatic HNSCC. We will evaluate the safety of intravenous cyclic STAT3 decoy, establish the recommended phase 2 dose (RP2D), and test the hypothesis that cyclic STAT3 decoy reduces expression of STAT3 target genes in paired tumor biopsies. Aim 2: To develop and optimize a platform for ultrasound-targeted MB-mediated delivery of cyclic STAT3 decoy. We will test the hypothesis that MB formulations with maximal cyclic STAT3 decoy loading and optimized acoustic parameters will cause knockdown of STAT3-regulated genes and cell death using in vitro and in in vivo HNSCC models. Aim 3: To determine the anti-tumor efficacy of intravenous cyclic STAT3 decoy combined with the US/MB platform developed in Aim 2 and the role of PTPRT mutation or hypermethylation in mediating responses. We will test the hypothesis that combined systemic and local delivery will improve responses, particularly in PTPRT mutant or hypermethylated tumors.